**2.2 Experimental set-up**

All experiments were done in 20 L anaerobic sequencing batch reactor followed by 10 L fixed bed reactor with gas outlet (Fig. 1). All the reactors were seeded with anaerobic acclimatized banana stem sludge. The anaerobic digestion system was varied at different reaction temperatures using water bath. The HRT and OLR for this system were 9 d and 4 g TS/l.d respectively. The process was conducted at ambient temperature for the first stage and thermophilic temperature for the second stage. Daily withdrawal of an appropriate volume from the reactor corresponding to the determined HRT or OLR was done by a draw-and-fill method. Biogas evolved from the fixed bed reactor was measured and collected in a gas holder by water displacement. Samples were collected and analyzed for performance evaluation.

Kinetics of Biogas Production from Banana Stem Waste 401

collection was done using daily water displacement. Methane content was analyzed using gas chromatography with thermal conductivity detector (GCTCD) with helium as the carrier gas. Acetic acid concentration (TVA) was determined using HPLC. Substrate concentration was measured as suspended solids according to the Standard Methods for The Examination of Water and Wastewater. 20 ml well-mixed sample was filtered through a weighed standard glass-fiber filter and the residue retained on the filter is dried to a constant weight at 103oC to 105oC. The increase in weight of the filter represents the total

Chen et al. (1978) developed a kinetic model on substrate utilization based on the Contois

= K ����

The kinetic model has been aptly used in many studies, notably in investigations on anaerobic digestion of high strength wastes (Mata-Alvarez et al. 1992; Sales et al. 2000).

> <sup>+</sup> � ����

<sup>+</sup> � ����

The kinetic parameters, μmax and K, were calculated with the aim of studying possible inhibition phenomena. Using the least squares method, the values for the kinetic parameters μmax and K can be obtained from the intercept and the slope of the adjusted lines. Thus, according to Eq. 20, μmax = 1/intercept, and K = slope/intercept. Through linear regression T

T=θ

S= So-S/S.

The kinetics of methane fermentation as proposed by Chen and Hashimoto (1978) is

� �1 � �

In this study the value of μmax and K calculated were 0.111 d-1 and 0.330 g/g respectively.

δ = ����

����

����

� + 1 (18)

� (19)

� (20)

���������� (21)

���� �

� � <sup>=</sup> � ����

θ = � ����

For a completely mixed system 1/µ= θ and 1/µm= θm. Therefore

vs S value of μmax and K could be determined (Fig. 2). Here

suspended solids (APHA 1989).

**3. Results and discussion** 

Equation (18) can be written as:

S is substrate total effluent

model as follows:

here

and

described by
